Firstly, take a peek at the sensors for any dirt or damage, like you mentioned. Additionally, ensure the wheel speed sensor rings are intact and free from debris.

Next, examine the brake fluid level and condition. Low brake fluid or contaminated fluid can trigger ABS warnings. Check for any leaks in the brake system as well.

Considering the mileage, it might also be prudent to inspect the overall condition of the brake system components, such as the master cylinder and brake lines.

Also, don't overlook the electrical connections tied to the ABS. Loose or corroded connections might be giving you false readings.
The ABS pump motor relay could be causing trouble. Test and inspect the relay for any signs of wear or malfunction.